1. Field of the Invention
The invention relates to an improved polyamide resin composition which includes from 0.1 to 20% by weight of a plasticising compound and to moulded hollow articles, which exhibit improved strength, i.e., burst pressure, that are produced by welding together discreet sections comprising said polyamide resin composition.
2. Description of Prior Art
It is known in the art to prepare polyamide-containing resin compositions from which moulded articles can be manufactured. Sometimes the requirements for the geometric shape of the moulded articles exceed the technical capabilities for moulding such an article in one piece or the moulding can only be carried out using a relatively costly and slow lost-core moulding process. As a result, alternative manufacturing processes have been developed to enable relatively complex-formed articles to be produced by first moulding parts of the article, for instance two half shells of a hollow article, and in a second step welding the shells together to form the desired article.
Difficulties have sometimes been encountered, however, in manufacturing articles with a sufficient strength to withstand the forces encountered in the utilization of such welded articles. A typical example is with air inlet manifolds for the automotive industry. In particular, weld failure can be a problem in applications where the welded article is subjected to an elevated internal pressure. This can happen, for example, when the article is an air intake manifold on an internal combustion engine, and the engine backfires.
An additional problem to overcome, besides that of weld failure is that in many cases the addition of compounds to the thermoplastic resin composition intended to increase the strength of a weld in the final article, may lead instead to a decrease in some other important property of the moulded article.
Surprisingly, it has now been found that including a specific weight percentage of a plasticising compound in polyamide resin compositions used for weldable moulded articles results in a significantly increased strength (as defined hereinafter), with minimal effect on other properties.